LINER LTC1844-SD 150ma, micropower, low noise, vldo linear regulator Datasheet

Final Electrical Specifications
LTC1844 Series
150mA, Micropower,
Low Noise, VLDO
Linear Regulator
May 2003
U
FEATURES
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
Very Low Dropout:
90mV at 150mA
30mV at 50mA (LTC1844-3.3)
Wide Input Voltage Range: 1.6V to 6.5V
Low 35µA Supply Current, Even in Dropout
Low Noise: 30µVRMS (10Hz to 100kHz)
±1.75% Voltage Accuracy Over Temperature,
Voltage and Current Ranges
Fast Transient Response
10nA Supply Current in Shutdown
Fixed Output Voltages: 1.5V, 1.8V, 2.5V, 2.8V, 3.3V
Adjustable Output Voltage: 1.25V to 6V
Output Current Limit
Reverse-Battery and Reverse-Current Protection
No Protection Diodes Needed
Stable with 1µF Output Capacitor
Stable with Ceramic Capacitors
Short-Circuit and Thermal Overload Protection
Low Profile (1mm) SOT-23 Package
U
APPLICATIO S
■
■
■
Bluetooth/802.11 Cards
PDAs and Notebook Computers
Portable Instruments and Battery-Powered Systems
Cellular Phones
U
■
The LTC®1844 Series are low noise VLDOTM (very low
dropout) linear regulators designed for low power/portable
applications. These regulators can operate from input
voltages as low as 1.6V. Typical output noise is only
30µVRMS and typical dropout for the LTC1844-3.3 is just
90mV at the maximum load current of 150mA, reducing to
30mV at 50mA.
The internal P-channel MOSFET pass transistor requires
no base current, allowing the device to draw only 35µA
during normal operation, independent of the dropout
voltage and load current. The quiescent current falls to a
negligible 10nA during shutdown.
Other features include high output voltage accuracy,
excellent transient response, stablity with ultralow ESR
ceramic capacitors as small as 1µF, reverse-battery and
reverse-current protection, short-circuit and thermal
overload protection and output current limiting.
The LTC1844 regulators are available in a low profile
(1mm) SOT-23 (ThinSOTTM) package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
VLDO and ThinSOT are trademarks of Linear Technology Corporation.
LTC1844-3.3 Dropout Voltage vs Load Current
TYPICAL APPLICATIO
120
Fixed Voltage Low Noise, VLDO Linear Regulator
1
VIN
3.3V TO 6.5V
1µF
OFF ON
IN
OUT
5
1µF
LTC1844-3.3
3
BYP
SHDN
GND
2
VOUT
3.3V
4
0.1µF
100
DROPOUT VOLTAGE (mV)
■
DESCRIPTIO
80
60
40
20
1844 TA01
0
0
25
50
75
100
IOUT (mA)
125
150
1844 TA02
1844ia
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
1
LTC1844 Series
W W
W
AXI U
U
ABSOLUTE
RATI GS (Note 1)
Supply Voltage (IN) ....................................... – 7V to 7V
Input Voltage
SHDN, BYP, ADJ .................................... – 0.3V to 7V
Output Voltage
OUT ........................................................ – 0.3V to 7V
OUT to IN .................................................. – 7V to 7V
Output Short-Circut Duration .......................... Indefinite
Operating Junction Temperature Range
(Notes 2, 10) .....................................–40°C to 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
U
U
W
PACKAGE/ORDER I FOR ATIO
IN 1
IN 1
5 OUT
SHDN 3
4 BYP
GND 2
BYP 3
4 ADJ
4 ADJ
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
5 OUT
IN 1
5 OUT
GND 2
GND 2
SHDN 3
TOP VIEW
TOP VIEW
TOP VIEW
TJMAX = 150°C, θJA = 250°C/ W, θJC = 90°C/ W
TJMAX = 150°C, θJA = 250°C/ W, θJC = 90°C/ W
TJMAX = 150°C, θJA = 250°C/ W, θJC = 90°C/ W
SEE THE APPLICATIONS INFORMATION SECTION
SEE THE APPLICATIONS INFORMATION SECTION
SEE THE APPLICATIONS INFORMATION SECTION
ORDER PART
NUMBER
S5 PART
MARKING
ORDER PART
NUMBER
S5 PART
MARKING
ORDER PART
NUMBER
S5 PART
MARKING
LTC1844ES5-1.5
LTC1844ES5-1.8
LTC1844ES5-2.5
LTC1844ES5-2.8
LTC1844ES5-3.3
LTF1
LTF2
LTF3
LTQK
LTF4
LTC1844ES5-SD
LTE8
LTC1844ES5-BYP
LTE9
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT + 0.5V, unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
VIN
Input Voltage
IIN
Quiescent Current
CONDITIONS
MIN
●
TYP
MAX
UNITS
6.5
V
35
55
80
µA
µA
0.01
1
µA
1.6
SHDN = VIN
●
IINSHDN
VIN Shutdown Supply Current
SHDN = 0V
VOUT%
Regulated Output Voltage
(Notes 3, 4, 5)
LTC1844-3.3
LTC1844-3.3
VIN = 3.8V to 6.5V, IOUT = 0mA to 150mA
VIN = 3.8V to 6.5V, IOUT = 0mA to 150mA
●
–1.50
–1.75
1.50
1.75
%VOUT
%VOUT
LTC1844-2.8
LTC1844-2.8
VIN = 3.3V to 6.5V, IOUT = 0mA to 150mA
VIN = 3.3V to 6.5V, IOUT = 0mA to 150mA
●
–1.50
–1.75
1.50
1.75
%VOUT
%VOUT
LTC1844-2.5
LTC1844-2.5
VIN = 3.0V to 6.5V, IOUT = 0mA to 150mA
VIN = 3.0V to 6.5V, IOUT = 0mA to 150mA
●
–1.50
–1.75
1.50
1.75
%VOUT
%VOUT
LTC1844-1.8
LTC1844-1.8
VIN = 2.3V to 6.5V, IOUT = 0mA to 150mA
VIN = 2.3V to 6.5V, IOUT = 0mA to 150mA
●
–1.50
–1.75
1.50
1.75
%VOUT
%VOUT
●
1844ia
2
LTC1844 Series
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT + 0.5V, unless otherwise noted. (Note 2)
SYMBOL
∆VLNR
∆VLDR
∆VDO
PARAMETER
Line Regulation (Notes 3, 5)
Load Regulation (Notes 3, 5)
Dropout Voltage (Notes 6, 7)
CONDITIONS
MIN
TYP
MAX
UNITS
LTC1844-1.5
LTC1844-1.5
LTC1844-1.5
VIN = 2.0V to 6.5V, IOUT = 0mA to 150mA
VIN = 2.2V to 6.5V, IOUT = 0mA to 150mA
VIN = 2.0V to 6.5V, IOUT = 0mA to 150mA
●
●
–1.50
–2.00
–2.50
1.50
2.00
2.00
%VOUT
%VOUT
%VOUT
LTC1844-BYP
LTC1844-BYP
LTC1844-BYP
VIN = 1.75V to 6.5V, IOUT = 0mA to 150mA
VIN = 2.2V to 6.5V, IOUT = 0mA to 150mA
VIN = 1.75V to 6.5V, IOUT = 0mA to 150mA
●
●
–1.50
–1.75
–3.50
1.50
1.75
1.75
%VOUT
%VOUT
%VOUT
LTC1844-SD
LTC1844-SD
LTC1844-SD
VIN = 1.75V to 6.5V, IOUT = 0mA to 150mA
VIN = 2.2V to 6.5V, IOUT = 0mA to 150mA
VIN = 1.75V to 6.5V, IOUT = 0mA to 150mA
●
●
–1.50
–1.75
–3.50
1.50
1.75
1.75
%VOUT
%VOUT
%VOUT
LTC1844-3.3
VIN = 3.4V to 6.5V, IL = 1mA
●
4
20
mV
LTC1844-2.8
VIN = 2.9V to 6.5V, IL = 1mA
●
4
20
mV
LTC1844-2.5
VIN = 2.6V to 6.5V, IL = 1mA
●
4
20
mV
LTC1844-1.8
VIN = 2.2V to 6.5V, IL = 1mA
VIN = 1.9V to 6.5V, IL = 1mA
VIN = 1.9V to 6.5V, IL = 1mA
●
4
4
4
20
20
30
mV
mV
mV
LTC1844-1.5
VIN = 2.2V to 6.5V, IL = 1mA
VIN = 1.6V to 6.5V, IL = 1mA
VIN = 1.6V to 6.5V, IL = 1mA
●
4
4
4
20
20
80
mV
mV
mV
LTC1844-BYP
VIN = 2.2V to 6.5V, IL = 1mA
VIN = 1.6V to 6.5V, IL = 1mA
VIN = 1.6V to 6.5V, IL = 1mA
●
4
4
4
20
20
80
mV
mV
mV
LTC1844-SD
VIN = 2.2V to 6.5V, IL = 1mA
VIN = 1.6V to 6.5V, IL = 1mA
VIN = 1.6V to 6.5V, IL = 1mA
●
●
4
4
4
20
20
80
mV
mV
mV
LTC1844-3.3
VIN = 3.8V, IOUT = 0mA to 150mA
●
9
20
mV
LTC1844-2.8
VIN = 3.3V, IOUT = 0mA to 150mA
●
9
20
mV
LTC1844-2.5
VIN = 3.0V, IOUT = 0mA to 150mA
●
9
20
mV
LTC1844-1.8
VIN = 2.3V, IOUT = 0mA to 150mA
●
9
20
mV
LTC1844-1.5
VIN = 2.2V, IOUT = 0mA to 150mA
VIN = 2.0V, IOUT = 0mA to 150mA
●
●
9
9
20
40
mV
mV
LTC1844-BYP
VIN = 2.2V, IOUT = 0mA to 150mA
VIN = 1.75V, IOUT = 0mA to 150mA
●
●
9
9
20
50
mV
mV
LTC1844-SD
VIN = 2.2V, IOUT = 0mA to 150mA
VIN = 1.75V, IOUT = 0mA to 150mA
●
●
9
9
20
50
mV
mV
LTC1844-3.3
IOUT = 50mA
IOUT = 150mA
●
●
30
90
55
150
mV
mV
LTC1844-2.8
IOUT = 50mA
IOUT = 150mA
●
●
35
105
60
165
mV
mV
LTC1844-2.5
IOUT = 50mA
IOUT = 150mA
●
●
45
135
75
200
mV
mV
LTC1844-1.8
IOUT = 50mA
IOUT = 150mA
●
●
85
230
120
300
mV
mV
LTC1844-1.5
IOUT = 50mA
IOUT = 150mA
●
●
115
350
160
450
mV
mV
LTC1844-BYP
IOUT = 50mA
IOUT = 150mA
●
●
45
135
75
200
mV
mV
LTC1844-SD
IOUT = 50mA
IOUT = 150mA
●
●
45
135
75
200
mV
mV
●
●
●
1844ia
3
LTC1844 Series
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT + 0.5V, unless otherwise noted. (Note 2)
SYMBOL
PARAMETER
ILIM
Output Current Limit
en
Output Voltage Noise
VSHDN
SHDN Input Threshold
tDELAY
Shutdown Exit Delay
CONDITIONS
●
MIN
TYP
160
350
mA
35
30
µVRMS
µVRMS
f = 10Hz to 100kHz, CBP = 0.1µF, COUT = 1µF, IL = 150mA
f = 10Hz to 100kHz, CBP = 0.1µF, COUT = 10µF, IL = 150mA
●
CBP = 0.01µF, COUT = 1µF, No load
CBP = 0.01µF, COUT = 1µF, No load
0.35
MAX
UNITS
0.65
0.9
V
70
100
200
µs
µs
●
°C
TSHDN
Thermal Shutdown Limit
∆TSHDN
Thermal Shutdown Hysteresis
IADJ
ADJ Pin Bias Current
(Notes 3, 8)
●
30
100
nA
IIRL
Input Reverse Leakage Current
LTC1844-3.3, LTC1844-2.8, LTC1844-2.5, LTC1844-1.8,
LTC1844-1.5, VIN = –5V, VOUT = 0V
●
200
500
µA
LTC1844-BYP, LTC1844-SD, VIN = –5V, VOUT = 0V
●
1000
1500
µA
Output Reverse Leakage Current
(Note 9)
VIN = 0V, VOUT = VOUT(NOMINAL)
VIN = 0V, VOUT = VOUT(NOMINAL)
0.01
●
0.1
1.2
µA
µA
VOSH
Start-Up Overshoot
RL = 1k, SHDN Rise Time ≤ 1µs
2
%VOUT
VRP
Output Ripple Rejection
(VIN – VOUT) = 1V (Avg), VRIPPLE = 0.5VP-P,
fRIPPLE = 120Hz, ILOAD = 100mA
60
dB
IORL
155
°C
10
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC1844 is tested and specified under pulse load conditions
such that TJ ≈ TA. The LTC1844E is guaranteed to meet performance
specifications from 0°C to 70°C. Specifications over the – 40°C to 125°C
operating junction temperature range are assured by design,
characterization and correlation with statistical process controls.
Note 3: The LTC1844 adjustable versions are tested and specifed for these
conditions with the ADJ pin connected to the OUT pin for a VOUT(NOMINAL)
of 1.252V.
Note 4: Operating conditions are limited by maximum junction
temperature. The regulated output voltage specification will not apply for
all possible combinations of input voltage and output current. When
operating at maximum input voltage, the output current range must be
limited. When operating at maximum output current, the input voltage
range must be limited.
Note 5: The LTC1844’s high precision degrades slightly at high
temperatures (TJ > 70°C) with input voltages below 2.2V. The lower output
voltage versions have been split into higher and lower accuracy input
voltage ranges to reflect this.
Note 6: To ensure adequate input supply voltage, the LTC1844 adjustable
versions are tested and specified for these conditions with an external
resistor divider (two 100k resistors) for an output voltage of 2.504V. The
external resistor divider will add a 5µA load on the output.
Note 7: Dropout voltage is (VIN – VOUT) when VOUT falls to 100mV below
its nominal value measured at VIN = VOUT + 0.5V. For example, the
LTC1844-3.3 is tested by measuring the VOUT at VIN = 3.8V, then VIN is
lowered until VOUT falls 100mV below the measured value. The difference
(VIN – VOUT) is then measured and defined as ∆VDO.
Note 8: ADJ pin bias current flows into the ADJ pin.
Note 9: Output reverse leakage current is tested with the IN pin grounded
and the OUT pin forced to the rated output voltage.
Note 10: This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
1844ia
4
LTC1844 Series
U
U
U
PI FU CTIO S
IN (Pin 1): Power for LTC1844 and Load. Power is supplied
to the device through the IN pin. The IN pin should be
locally bypassed to ground if the LTC1844 is more than a
few inches away from another source of bulk capacitance.
In general, the output impedance of a battery rises with
frequency, so it is usually adviseable to include an input
bypass capacitor in battery-powered circuits. A capacitor
in the range of 0.1µF to 1µF is usually sufficient. The
LTC1844 is designed to withstand reverse voltages on the
IN pin with respect to both ground and the output pin. In
the case of a reversed input, which can happen if a battery
is plugged in backwards, the LTC1844 will act as if there
is a large resistor in series with its input with only a small
amount of current flow.
GND (Pin 2): Ground and Heat Sink. Solder to a ground
plane or large pad to maximize heat dissipation.
SHDN (Pin 3, Fixed and SD Devices): Shutdown, Active
Low. This pin is used to put the LTC1844 into shutdown.
The SHDN pin current is typically less than 10nA. The
SHDN pin cannot be left floating and must be tied to the
input pin if not used. If reverse-battery protection is
desired, the SHDN pin must be tied to the input pin through
a large value resistor (10k to 1M).
ADJ (Pin 4, Adjustable Devices): Output Adjust. For the
adjustable versions of the LTC1844, this is the input to the
error amplifier. It has a typical bias current of 30nA flowing
into the pin. The ADJ pin reference voltage is 1.25V
referenced to ground. The output voltage range is 1.25V to
6V and is typically set by connecting ADJ to a resistor
divider from OUT to GND. See Figure 2.
BYP (Pin 4, Fixed/Pin 3, BYP Devices): Noise Bypass.
The BYP pin is used to augment the internal noise filter to
improve low noise performance. A small low leakage
bypass capacitor from this pin to ground will filter the input
of the error amplifier to lower the output voltage noise.
Any value may be used; larger values will result in lower
output noise, but will increase initial power-up time.
Shutdown exit delay time after a brief shutdown (<10ms)
will not be affected. If not used, this pin must be left
unconnected.
OUT (Pin 5): Voltage Regulated Output. The OUT pin
supplies power to the load. A minimum output capacitor of
1µF is required to ensure stability. Larger output capacitors
may be required for applications with large transient loads
to limit peak voltage transients. See the Applications
Information section for more information on output
capacitance.
1844ia
5
LTC1844 Series
U
W
U U
APPLICATIO S I FOR ATIO
The LTC1844 family are a series of 150mA ultralow
dropout regulators with micropower quiescent current
and shutdown. The devices are capable of supplying
150mA at a dropout voltage of 90mV (LTC1844-3.3, see
Electrical Characteristics for dropout voltage of other
versions). Output voltage noise is as low as 30µVRMS over
a 10Hz to 100kHz bandwidth with the addition of a 0.1µF
bypass capacitor. The low operating quiescent current
(35µA) drops to 10nA in shutdown.
LOAD CURRENT (mA)
OUTPUT VOLTAGE
DEVIATION (V)
In addition to the low quiescent current, the LTC1844
regulators incorporate several protection features which
make them ideal for use in battery-powered systems. The
devices are protected against both reverse input voltages
and reverse voltages from output to input (reverse current
protection). The devices also include current limit and
thermal overload protection, and will survive an output
short circuit indefinitely. The fast transient response overcomes the traditional tradeoff between dropout voltage,
quiescent current and load transient response inherent in
most regulators by using a proprietary new architecture
(see Figure 1).
VIN = 3V
CIN = 1µF
COUT = 1µF
0.04
0.02
Adjustable Operation
The adjustable version of the LTC1844 has an output
voltage range of 1.25V to 6V. The output voltage is set by
the ratio of two external resistors as shown in Figure 2. The
device servos the output to maintain the ADJ pin voltage
at 1.25V (referenced to ground). The current in R1 is then
equal to 1.25V/R1 and the current in R2 is the current in R1
plus the ADJ pin bias current. The ADJ pin bias current,
30nA at 25°C, flows through R2 into the ADJ pin. The
output voltage can be calculated using the formula in
Figure 2. The value of R1 should be no greater than 1M to
minimize errors in the output voltage caused by the ADJ
pin bias current. Note that in shutdown the output is turned
off and the divider current will be zero once COUT is
discharged.
Adjustable devices are tested and specified with the ADJ
pin tied to the OUT pin for an output voltage of 1.25V.
Specifications for output voltages greater than 1.25V will
be proportional to the ratio of the desired output voltage to
1.25V: VOUT/1.25V. For example, load regulation for an
IN
VIN
0
OUT
LTC1844
VOUT
R2
CFF
+
ADJ
–0.02
GND
–0.04
R1
1844 F02
 R2 
VOUT = 1.25V  1 +  + (IADJ )(R2)
 R1
VADJ = 1.25V
50
0
0
10 20 30 40 50 60 70 80 90 100
TIME (µs)
IADJ = 30nA AT 25°C
OUTPUT RANGE = 1.25V TO 6V
CFF OPTIONAL
1844 F01
Figure 1. LTC1844-2.5 Transient Response 1mA to 50mA to 1mA
Figure 2. Adjustable Operation
1844ia
6
LTC1844 Series
U
W
U U
APPLICATIO S I FOR ATIO
output current change of 1mA to 100mA is – 4mV typical
at VOUT = 1.25V. At VOUT = 5V, load regulation is:
(5V/1.25V)(– 4mV) = –16mV
Because the ADJ pin is relatively high impedance (depending on the resistor divider used), stray capacitance at this
pin can introduce significant phase shift in the error
amplifier loop. The PCB layout should be designed to
absolutely minimize the capacitance seen at the ADJ pin.
To ensure stability over all operating conditions when
utilizing large divider resistors, it may be necessary to use
a small ceramic feedforward capacitor (~1000pF) in parallel with the upper divider resistor (see CFF in Figure 2). As
an added bonus, this capacitor will improve transient
response.
Bypass Capacitance and Low Noise Performance
A bypass capacitor can optionally be connected from the
BYP pin to ground to lower output voltage noise. A good
quality low leakage capacitor is recommended. This capacitor will bypass the input of the error amplifier, providing a low frequency noise pole. The noise pole provided by
this bypass capacitor will lower the output voltage noise to
as low as 30µVRMS with the addition of a 0.1µF capacitor.
Initial regulator power-up time is inversely proportional to
the size of the bypass capacitor, slowing to 10ms with a
0.1µF capacitor and 10µF output capacitor. However, the
LTC1844 does not discharge the bypass capacitor when
put into shutdown and thus the shutdown exit delay can be
much shorter (≈70µs) than initial power-up time if the
shutdown duration is brief (<10ms). The maximum shutdown duration required to allow fast shutdown exit is
determined by the capacitor leakage current, thus a low
leakage bypass capacitor is recommended.
Output Capacitance and Transient Response
The LTC1844 regulators are designed to be stable with a
wide range of output capacitors. The ESR of the output
capacitor affects stability, most notably with small capacitors. A minimum output capacitor of 1µF with an ESR of
0.3Ω or less is recommended to ensure stability. The
LTC1844 is a micropower device and output transient
response will be a function of output capacitance. Larger
values of output capacitance decrease the peak deviations
and provide improved transient response for larger load
current changes. Note that bypass capacitors used to
decouple individual components powered by the LTC1844
will increase the effective output capacitor value. The
shaded region of Figure 3 defines the region over which
the LTC1844 regulators are stable. The maximum ESR
allowed is 0.3Ω. High ESR tantalum and electrolytic capacitors may be used, but a low ESR ceramic capacitor
must be in parallel at the output. There is no minimum ESR
requirement.
Extra consideration must be given to the use of ceramic
capacitors. Ceramic capacitors are manufactured with a
variety of dielectrics, each with different behavior across
0.40
0.35
ESR (Ω)
0.30
0.25
0.20
STABLE REGION
0.15
0.10
0.05
0
0.33
1
3.3
10
33
OUTPUT CAPACITANCE (µF)
100
1844 F03
Figure 3. Stability
1844ia
7
LTC1844 Series
U
U
W
U
APPLICATIONS INFORMATION
temperature and applied voltage. The most common dielectrics used are Z5U, Y5V, X5R and X7R. The Z5U and
Y5V dielectrics are good for providing high capacitances
in a small package, but exhibit strong voltage and temperature coefficients as shown in Figures 4 and 5. When
used with a 5V regulator, a 10µF Y5V capacitor can exhibit
an effective value as low as 1µF to 2µF over the operating
temperature range. The X5R and X7R dielectrics result in
more stable characteristics and are more suitable for use
as the output capacitor. The X7R type has better stability
across temperature, while the X5R is less expensive and
is available in higher values.
20
Additionally, some ceramic capacitors have a piezoelectric
response. A piezoelectric device generates voltage across
its terminals due to mechanical stress, similar to the way
a piezoelectric accelerometer or microphone works. For a
ceramic capacitor the stress can be induced by vibrations
in the system or thermal transients. The resulting voltages
produced can cause appreciable amounts of noise, especially when a ceramic capacitor is used for noise bypassing. A ceramic capacitor produced Figure 6’s trace in
response to light tapping from a pencil. Similar vibrationinduced behavior can masquerade as increased output
voltage noise.
LTC1844-2.8
COUT = 10µF
CBYP = 0.01µF
ILOAD = 100mA
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
CHANGE IN VALUE (%)
0
X5R
–20
VOUT
500µV/DIV
–40
–60
Y5V
–80
100ms/DIV
–100
0
2
4
14
8
6
10 12
DC BIAS VOLTAGE (V)
1844 F06
16
Figure 6. Noise Resulting from Tapping on a Ceramic Capacitor
1844 F04
Figure 4. Ceramic Capacitor DC Bias Characteristics
40
The power handling capability of the device will be limited
by the maximum rated junction temperature (125°C). The
power dissipated by the device will be the output current
multiplied by the input/output voltage differential:
(IOUT)(VIN – VOUT).
CHANGE IN VALUE (%)
20
X5R
0
–20
–40
Y5V
–60
–80
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
–100
50
25
75
–50 –25
0
TEMPERATURE (°C)
Thermal Considerations
100
125
1844 F05
Figure 5. Ceramic Capacitor Temperature Characteristics
The LTC1844 series regulators have internal thermal limiting designed to protect the device during momentary
overload conditions. For continuous normal conditions,
the maximum junction temperature rating of 125°C must
not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to
ambient. Additional heat sources mounted nearby must
also be considered.
1844ia
8
LTC1844 Series
U
U
W
U
APPLICATIONS INFORMATION
For surface mount devices, heat sinking is accomplished
by using the heat-spreading capabilities of the PC board
and its copper traces. Copper board stiffeners and plated
through holes can also be used to spread the heat generated by power devices.
Table 1 lists thermal resistance for several different board
sizes and copper areas. All measurements were taken in
still air on 3/32" FR-4 board with one ounce copper.
Table 1. Measured Thermal Resistance
COPPER AREA
TOPSIDE*
BACKSIDE
2
BOARD AREA
2500mm
1000mm
2500mm
2
2500mm
125°C/W
225mm2
2500mm2
2500mm2
130°C/W
2
2500mm
2
2
135°C/W
2500mm
2
2
150°C/W
2
100mm
2
50mm
2
125°C/W
2
2500mm
2500mm
2500mm
0.135W(150°C/W) = 20.3°C
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
T = 50°C + 20.3°C = 70.3°C
Protection Features
THERMAL RESISTANCE
(JUNCTION-TO-AMBIENT)
2
2500mm
copper area. The junction temperature rise above ambient
will be approximately equal to:
*Device is mounted on topside.
Calculating Junction Temperature
Example: Given an output voltage of 3.3V, an input voltage
of 4V to 6V, an output current range of 0mA to 50mA and
a maximum ambient temperature of 50°C, what will the
maximum junction temperature be?
The power dissipated by the device will be equal to:
IOUT(MAX)(VIN(MAX) – VOUT)
where:
IOUT(MAX) = 50mA
VIN(MAX) = 6V
So:
P = 50mA(6V – 3.3V) = 0.135W
The power dissipated by the LTC1844’s quiescent current
(240µW) is insignificant. The thermal resistance will be in
the range of 125°C/W to 150°C/W depending on the
The LTC1844 regulators incorporate several protection
features which make them ideal for use in battery-powered
circuits. In addition to the usual protection features associated with monolithic regulators, such as current limiting
and thermal limiting, the devices are protected against
reverse input voltages and reverse voltages from output to
input.
Current limit protection and thermal overload protection
are intended to protect the device against current overload
conditions at the output of the device. For normal operation, the junction temperature should not exceed 125°C.
The input of the device will withstand input voltages of
– 7V. Current flow into the device will be limited to less
than 500µA (typically less than 200µA) and only a small
negative voltage will appear at the output (~ –300mV with
no load). The LTC1844 will protect both itself and the load
against batteries plugged in backward.
In circuits where a backup battery is required, several
different input/output conditions can occur. The output
voltage may be held up externally while the input is either
pulled to ground, pulled to some intermediate voltage or
left open circuit. The LTC1844 features reverse current
protection to limit current draw from any supplementary
power source at the output. When VIN is pulled to ground
or is left open circuit, IIN and IOUT are less than 0.1µA for
VOUT = 0V to 7V.
1844ia
9
LTC1844 Series
U
U
W
U
APPLICATIONS INFORMATION
When VIN is held constant and VOUT varied, current flow
will follow the curves shown in Figure 7. With VOUT held
below VOUT(NOM), the LTC1844 will be in current limit
trying to pull VOUT up. With VOUT held between VOUT(NOM)
and VIN, IIN will be at the normal quiescent current level
and IOUT will be 1µA to 2µA. As VOUT is pulled above VIN,
IOUT temporarily increases to 30µA until the reverse current protection circuitry activates and reduces IOUT to less
than 10µA.
50
100
LTC1844-2.8
TJ = 25°C
VIN = 3.3V
CURRENT FLOWS
INTO PINS
45
40
30
IN CURRENT
LIMIT BELOW
2.8V
25
20
15
IOUT
10
80
70
50
40
30
IIN
10
0
4
3
2
5
OUTPUT VOLTAGE (V)
IIN
20
5
1
IN CURRENT
LIMIT ABOVE
2.7V
60
0
0
LTC1844-2.8
TJ = 25°C
VOUT = 2.7V
CURRENT FLOW
INTO PINS
90
CURRENT (µA)
35
CURRENT (µA)
Alternatively, when VOUT is held constant and VIN varied,
current flow will follow Figure 8’s curves. IOUT will be less
than 10µA at all times except for a brief spike just below
2.7V before the reverse current protection circuitry activates.
6
7
1844 F07
Figure 7. Reverse Current vs Output Voltage
IOUT
0
0.5
1.5
2.0
1.0
INPUT VOLTAGE (V)
2.5
3.0
1844 F08
Figure 8. Reverse Current vs Input Voltage
1844ia
10
LTC1844 Series
U
PACKAGE DESCRIPTIO
S5 Package
5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
0.62
MAX
0.95
REF
2.90 BSC
(NOTE 4)
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.45 TYP
5 PLCS (NOTE 3)
0.95 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
0.09 – 0.20
(NOTE 3)
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
1.90 BSC
S5 TSOT-23 0302
1844ia
11
LTC1844 Series
RELATED PARTS
PART NUMBER
LT1761
LT1762
DESCRIPTION
100mA, Low Noise LDO in ThinSOT
150mA, Low Noise LDO
LT1763
LT1764A
500mA, Low Noise LDO
3A, Fast Transient Response, Low Noise LDO
LT1962
300mA, Low Noise LDO
LT1963A
1.5A Low Noise, Fast Transient Response LDO
LT1964
LT3150
200mA, Low Noise, Negative LDO
Fast Transient Response, VLDO Regulator
Controller
COMMENTS
300mV Dropout Voltage, Low Noise: 20µVRMS, VIN = 1.8V to 20V, ThinSOT
300mV Dropout Voltage, Low Noise: 20µVRMS, VIN = 1.8V to 20V,
MS8 Package
300mV Dropout Voltage, Low Noise: 20µVRMS, VIN = 1.8V to 20V, SO-8 Package
340mV Dropout Voltage, Low Noise: 40µVRMS, VIN = 2.7V to 20V,
TO-220 and DD Packages
270mV Dropout Voltage, Low Noise: 20µVRMS, VIN = 1.8V to 20V,
MS8 Package
340mV Dropout Voltage, Low Noise: 40µVRMS, VIN = 2.5V to 20V, TO-220, DD,
SOT-223 and SO-8 Packages
340mV Dropout Voltage, Low Noise 30µVRMS, VIN = –1.8V to – 20V, ThinSOT
0.035mV Dropout Voltage via External FET, VIN: 1.3V to 10V
1844ia
12
Linear Technology Corporation
LT/TP 0503 1K REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2003
Similar pages